In the utilization of catheters to diagnose and treat various medical disorders, it is very often required that more than one device be used during the procedure. Because positioning of the catheter at the desired location may be difficult, time consuming, or critical or pose a high risk, techniques have been developed that facilitate exchange of catheter devices.
The most common technique for catheter exchange employs a very long guidewire called an exchange wire. In this technique the exchange wire is placed within a central lumen of a catheter that has been previously positioned within the body. To maintain the desired position, the exchange wire is advanced while the catheter is simultaneously withdrawn. Once the catheter is completely out of the body, it is removed from the exchange wire. A second catheter is then positioned over the exchange wire, and, once the catheter is completely on the exchange wire, it is then advanced to the desired site in the body. This over-the-wire technique for catheter exchange is considerably time consuming, and it requires at least two operators to effect the exchange. In addition, the very long exchange wire extends beyond the sterile field, which adds to the risk of contamination during the procedure.
U.S. Pat. No. 4,762,129 to Bonzel and U.S. Pat. No. 5,040,548 to Yock describe balloon angioplasty catheters that can be exchanged over a standard length guidewire. These catheters are called monorail catheters, and they are designed such that only a relatively short segment of the distal end of the catheter is advanced over the guidewire, i.e., the catheter has a lumen to receive the guidewire that extends from the distal tip of the catheter to a location proximal to the balloon. Since the length of the guidewire used is only about half that of an exchange wire, the catheter exchange can be done more quickly, and a single operator may do the exchange. However, since a much shorter segment of the catheter is concentric to the guidewire, the monorail-type catheters have diminished axial support for tracking the guidewire (trackability) and transmission of axial or longitudinal forces (pushability).
In addition to the drawbacks cited above, both of the catheter exchange techniques described above have two additional shortcomings--increased diameter of the catheters to accommodate the guidewire, and risk of vessel trauma resulting from repeated catheter passages. In a number of applications, over-the-wire catheters are too large to be placed at the desired location. In these applications, smaller catheters, whose diameters have been reduced by eliminating the guidewire lumen, have been required. Exchange with these prior art systems consisted essentially of starting over after the first catheter was removed. This is often time consuming, and there is an increased risk of complications resulting from vessel trauma. U.S. Pat. Nos. 4,944,740 and 4,976,689 addressed the trauma issue by providing an outer tubular sheath concentric to an inner catheter. However, this system would have very limited application in small blood vessels, as the system itself would occlude the blood vessel and cause ischemic complications. Moreover, the outer tubular sheath must be used as a system with its inner catheter; if another catheter or guidewire was used initially, this system could not make the exchange.